This invention relates generally to the production of curved objects and particularly to apparatus for verifying the acceptability of the curvature of curved objects, such as kinescope shadow masks after such masks are welded to support frames.
A color picture tube includes a color selection electrode, commonly called a shadow mask, which causes the electron beams to impact phosphors of the proper light emitting color. The viewing screen of a color picture tube is curved along at least one axis. Accordingly the shadow mask must have essentially the same curvature as the phosphor screen. Shadow masks are fabricated from thin conductive metal and include a large plurality of apertures. For these reasons shadow masks are flimsy and easily deformed. A shadow mask therefore is welded to a sturdy frame which lends physical support to the mask. A plurality of apertured leaf springs are welded to the sides of the shadow mask frame. The apertures in the springs engage studs which are embedded in the sidewalls of the glass faceplate panel to support the shadow mask at a particular distance from the screen. The space between the screen and the shadow mask is called the Q space and is a very critical dimension because variations in the Q spacing can cause the electron beams to impact phosphors of the wrong light emitting color causing discoloration of the visual display.
The Q spacing is critical and therefore any one of several things can occur to cause electron misregistration and discoloration resulting therefrom. For example, concave or convex dents in the shadow mask can cause the electron beams to impact the wrong color of phosphor. Also, the shadow mask and shadow mask frame can be improperly aligned prior to welding the mask to the frame causing the mask to be tilted with respect to the screen. Additionally the welding process adds heat to both the frame and shadow mask and therefore warpage can cause misregistration of the electron beams.
For these reasons there is a need for an apparatus for verifying the acceptability of the curvature of a curved object immediately following the processing step. The present invention fulfills this long felt need.